1. Field of the Invention
The present invention relates generally to systems and methods for disinfection and decontamination of surfaces and, in particular, to systems and methods which employ pulses of Ultra Violet (UV) light for surface disinfection and decontamination.
2. Antecedents of the Invention
UV radiation has been employed for disinfection and decontamination of surfaces, air and liquids. It is considered to be one of the best non-contact decontamination processes. The UV-C region of the UV spectrum has been found to be the most lethal to microorganisms; the strongest germicidal effects have been reported to be in the wave-length from 200 nm to 280 nm. This part of the spectrum has been found lethal to several ranges of microorganisms.
Traditionally, UV radiation for disinfection employed medium pressure mercury vapor lamps to generate UV radiation. In recent decades, pulsed xenon lamps have been found to be much more effective than other UV light emitting technology.
There are several reasons which play a critical role in the efficacy of pulsed xenon UV radiation used for disinfection. One is the broadband spectrum of UV discharge in xenon lamps.
Another reason is that pulsed xenon UV systems have the capability of discharging several megawatts of UV energy in micro-seconds or milliseconds, causing irreversible changes in the cellular level in the microorganisms exposed.
Pulsed xenon UV light technology was first developed in Japan. In 1984 Hiramoto patented pulsed UV light technology for sterilization applications. Since then it has been employed for various applications involving disinfection and decontamination
The spectral output of an UV xenon lamp is very similar to that of sunlight. It goes from 180 nm to 1100 nm, with some major spikes in visible region of the spectrum. The xenon UV discharge lamp can be designed in different geometries to best fit the application. That makes the pulsed UV system very flexible. The system can be tailored to best fit the application in terms of energy requirement.
The energy dissipated can be controlled in terms of number of pulses, energy per pulse and pulse width. Since the xenon UV flash tube discharges in pulses, the existing systems are not a good fit for applications involving fast moving targets.
Characteristics of Pulsed UV Light Relevant to Disinfection
Pulsed light energy is measured in fluence and is related to fluence rate. Fluence rate is the total radiant energy falling on small transparent sphere containing the target from all possible directions, divided by the cross section of the target. It is generally expressed in W/m2.
Fluence can be defined as the product of fluence rate, exposure time in seconds and total amount of energy incident on the target during the exposure time. It is expressed in J/m2 or J/cm2.F=e*t*f 
Where F is the fluence (J/cm2), “e” is the energy per pulse J/cm2/pulse, “t” is the time in seconds and “f” is the frequency.
A well-known general rule in photochemistry, the Bunsen-Roscoe reciprocity law, states that the extent of photochemical effects on living beings is determined by cumulative irradiance. Accordingly, for disinfection applications, the current methods and apparatuses using pulsed UV light technology tend to employ high UV energy per pulse, and relatively low frequencies of 1-2 pulses per second.
Typical prior art systems employing pulsed xenon UV lamps for disinfection are disclosed in U.S. Pat. Nos. 9,093,258, 8,872,669 and 9,165,756 as well as U.S. Patent Application Publication No. 2013-0330235. These systems suffered from various shortcomings, however.
They employed lower pulse frequency (typically below 2 Hz), therefore took longer time to inactivate germs. They employed high discharge energy per each pulse (typically more than 500 joules), therefore the generated noise level was high (manifested as loud popping sounds) causing disturbance around the treated area. The high energy of discharge also generated an unsafe amount of ozone, which had to be removed by specialized fans and filters, contributing to additional cost, complexity and noise. They employed a 360 degree, all around flashing UV light geometry, making them suitable for entire room disinfection, but causing energy to be wasted if only certain limited surfaces were in need of treatment. To compensate for the wasted energy, they required more operating time in each room, hence relatively high overall energy consumption. Due to their high level of ozone generation, they required additional filtration and power consuming auxiliary components such as blower motors, etc., which resulted in higher energy consumption per unit time. They employed optical filters (to filter out the visible light produced by the lamps), which did not fully eliminate visible pulsating light while decreasing the UV capability of the apparatus.
Thus, there was an unmet need for systems and methods of pulsed xenon UV disinfection that do not suffer from the shortcomings of the antecedents referenced above. There was a further need for such systems to work more rapidly, to be able to focus more effectively only on certain targeted contaminated surfaces, and to be more energy efficient.